Two extensive studies were made to evaluate
vicinity of the bubbler, the temperatures become
the effects of bubbler systems in the DuluthSu-
very uniform over the depth due to the mixing
perior Harbor (Sydor et al. 1974, Swain et al. 1975).
by the bubbler-induced flows and are contracted
Neither study directly addressed fish movement
with the slight stratification that exists in undis-
and populations in detail, but since no apparent
turbed portions of the harbor. Swain et al. (1975)
adverse changes were observed in the many wa-
observed an increase in dissolved oxygen after
ter quality variables studied, it is reasonable to
the bubbler was turned on but a nearly similar
conclude that there would be no adverse effects
increase 150 ft away. Whether the increase is due
on fish due to changes in the surrounding envi-
to bubbler operation or other effects is unclear,
ronment.
but there were no deleterious effects due to the
In JanuaryApril 1976 heated water from a
bubbler operation. The National Biocentric, Inc.
power plant was released from a diffuser pipe in
(1973) study found slightly higher oxygen con-
the vicinity of the Saginaw Bay shipping channel
tents at lower depths in the region of the bubbler
for the purpose of locally reducing the ice cover
but noted that the small increase could not be
thickness. The water was released over short du-
expected to much enhance fish populations. The
rations, and the excess water temperature was
Swain et al. (1975) study concluded that there was
1C or less. The warmer water collected near the
no increase in levels of major water quality vari-
bottom and had little effect on the ice cover. (How-
ables due to bubbler operation but did find a ten-
ever, if a bubbler had been used to deliver the
dency to damp large, naturally occurring oscilla-
water to the ice cover, the suppression could have
tions of the variables measured. In summary, no
been significant.) Over the period 19721976
adverse effects on water quality were found, while
baseline and operational data were collected to
some slight evidence of beneficial effects were
evaluate the effects of the heated water release
found. In most studies other effects greatly domi-
on the local benthic communities and fish (Ar-
nated the small influence of the bubbler opera-
gyle 1974, Hatcher 1977). No differences in popu-
tion. These include effects of vessel traffic and
lations of a wide variety of fauna were found that
natural events such as runoff, which cause more
could be attributed to the heated water except
marked changes.
one. Statistical tests and comparisons suggested
the possibility that the under-ice release of warm
water resulted in increased densities of immature
ICE CONTROL STRUCTURES
oligochaetes (tubificids). The study did provide
This summary of ice control structures and re-
a good picture of the distribution and diversity
of species present in the Saginaw Bay channel area.
lated studies under the Great Lakes Winter Navi-
gation Program is presented to the extent pos-
The question of possible sediment resuspension
in the vicinity of bubbler systems was considered
sible in chronological order. The use of ice booms
by Swain et al. (1975), who found that any pos-
as an ice control tool for winter navigation did
not appear to be recognized at first. What was
sible resuspension would be extremely small when
compared to other factors that cause resuspension
recognized was that navigable openings were
needed in certain ice booms that the hydroelec-
in the harbor, such as storm effects, natural run-
off effects, vessel traffic effects, and industrial and
tric power companies set across the St. Lawrence
municipal inflows. Sydor et al. (1974) measured
River in early winter to ensure dependable elec-
tric power generation in winter. One scheme was
currents in the vicinity of an operating bubbler
system and described them as gentle near the bot-
to leave part of the boom open but connected,
and then pull it closed after the last ship passed
tom. A study by National Biocentric, Inc. (1973)
similarly found that operation of a bubbler did
through using an electric winch mounted on a
not appear to be effective in resuspending organic
cell structure (USACE 1969). Before long it was
seen that criteria required for the design of ice
material, sediments or nonsoluble nutrients.
Water quality during the operation of bubbler
booms to retain ice on the St. Lawrence Seaway,
St. Marys River and others were not available. In
systems in the Duluth Superior Harbor was con-
sidered in detail by National Biocentric, Inc. (1973),
particular, information on the magnitude of ice
Sydor et al. (1974) and Swain et al. (1975), including
forces was lacking. The task of making these de-
terminations fell to the Ice Engineering Work
monitoring of temperature, dissolved oxygen and
an extensive list of chemicals. In the very near
Group.
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